m117 560SEL Odd Behavior
 

Hey everyone,

I figured someone out here might be able to help solve this problem.

My buddys 560SEL acts wimpy, out of power, vacuum loss (measured by the econo gauge, stalls sometimes, when it hits 60C. Up until this point the car run fine. Once it passes this mark on the temp gauge all is right with the work again..

Anyone have any thoughts on this?

It has a recent tune up, new ovp, fuel pump relay....

Kris, light that car on fire already. :)

Replace the temp sensors that the ignition unit uses as well as the one for the engine ECU. Temperature related open circuit in the sensor makes the car think it is at a high or low temp. Mixture gets all screwed up. When the car warms up the sensor begin working properly and all is right with the world.

The 4-pin CIS temp sensor has already been replaced. You do make a valid point though. I wonder if we were to wire in a resistor (= to 80C) if the car would exhibit the same behavior...

That would be a good diagnostic test.

My 1986 500 sl had the exact problem. After testing all the systems, ignition, fuel, replacing lots of parts, I cut a hole in the exhaust before the cat converter and the problems all went away. Check for exhaust back pressure.

Wait, so it runs good cold until it hits 60, then runs crappy, then runs good again once it gets up to temp?


That totally sounds like a bad temp sensor. My 300SE is doing something similar right now, but I've been so busy with the heater core that I haven't looked at it yet. However, mine just runs like crap until it gets warmed up at this point. Temp sensors are testable.